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Low-Gravity Environment
Published in Basil N. Antar, Vappu S. Nuotio-Antar, Fundamentals of Low Gravity Fluid Dynamics and Heat Transfer, 2019
Basil N. Antar, Vappu S. Nuotio-Antar
An object released motionless relative to the spacecraft at some distance from the center of mass along the radial vector from the center of the Earth will have an orbit slightly different from that of the spacecraft. Since the velocity required to maintain a circular orbit varies inversely with the square root of the distance from the center of the Earth, this object will have a slightly different velocity which will put it into an elliptical orbit with a different period. This trajectory will cause the object to slowly drift away from its initial position as the spacecraft describes its orbit around the Earth. The accelerations required to continuously alter the trajectories of such interior objects to keep them in the same relative configuration are of the order 10–7g0 for each meter of radial displacement from the spacecraft’s center of mass.
Satellite Systems
Published in Jerry D. Gibson, The Communications Handbook, 2018
An unmanned launch vehicle usually places the satellite directly into an elliptical Earth orbit that is called a transfer orbit. The highest point in this elliptical orbit is called the apogee and the lowest point is called the perigee. The launch is designed to provide an apogee that is the same height as the geostationary orbit. A special rocket in the satellite provides the acceleration needed to transfer the satellite from an elliptical orbit into a geostationary orbit. This special rocket in a satellite is called an apogee motor or an apogee kick motor (AKM). Elliptical orbits have an angle of inclination that corresponds to the latitude of the launch site. For example, satellites launched from Cape Canaveral, Florida, have an elliptical orbit with an inclination of approximately 27.5°. The apogee motor must also provide the acceleration to change the angle of inclination to zero as a satellite's orbit is changed from elliptical to geostationary.
Solar Radiation
Published in T. Agami Reddy, Jan F. Kreider, Peter S. Curtiss, Ari Rabl, Heating and Cooling of Buildings, 2016
T. Agami Reddy, Jan F. Kreider, Peter S. Curtiss, Ari Rabl
Another source of deviation between solar time and local civil time is due to the nature of the earth’s orbital motion around the sun. The elliptical orbit induces changes in the orbital angular speed of the earth (according to Kepler’s laws). Solar noon is the time when the sun reaches the highest point in the sky; it can differ from noon of local civil time by as much as one-quarter hour. The difference between solar noon and noon of local civil time is called the “equation of time” Et. It is a function of the time of year (plotted in Figure 4.3) and can be approximated by Et=9.87×sin2B−7.53×cosB−1.5×sinB(min)withB=360°×n−81364fornthdayofyear
Plasma Waves Around Venus and Mars
Published in IETE Technical Review, 2021
The PWS observation of plasma wave electric field and spacecraft potential is shown in Figure 33 during 4th elliptical orbit around Mars and Figure 34 with circular orbit around Mars. The objective of these measurements was to locate the boundaries of bow-shock and planetopause as indicated in the respective figures. The electric field spectrogram, the spacecraft potential, the RMS Langmuir Probe current fluctuation (in range 0.1–50 Hz), high frequency fluctuations in this collected signal, the electric field intensities averaged over middle frequency bandwidth (100 Hz–6 kHz) fluctuation of this and the filtered electric field in the range 0.2–10 Hz are shown in both the Figures 32 and 33 from top panel to bottom and the electric field levels are shown in dB above 1 μVm−1Hz−1/2. The vertical red lines show the inbound bow shock and planetopause crossings [90].